Process for preparing aromatic haloamines from aromatic nitroamines

ABSTRACT

Process for preparing aromatic haloamines comprises hydrogenating the corresponding halogen-substituted nitroaromatic compound in the presence of a platinum group metal catalyst, said catalyst being modified with a metal selected from the group Pb, Bi, or Ag. The catalysts are effective at relatively mild conditions and the hydrogenation is effected with minimum dehalogenation.

I United States Patent [151 3,666,8 1 3 Hindin et a]. [451 May 30, 1972 [54] PROCESS FOR PREPARING AROMATIC [56] References Cited HALOANIINES FROM AROMATIC UNITED STATES PATENTS NITROAMINES 3,253,039 5/1966 Rylander et a1 ..260/580 [72] Inventors: Saul G. l-lindin, Mendham; Daniel L. Bair,

Roselle Park; Duane R. Steele, Newark, all Primary Examiner joseph Rebold of Ni Assistant Examiner-Donald M. Papuga [73] Assignee: Engelhard Minerals & Chemicals Corpora- Atmmey samuel Kahn and Mmam Leff non, Newark, NJ. ABSTRACT F'l d: A 27 1969 [22] 1 e Process for preparing aromatic haloamincs comprises [21] Appl. No.: 853,503 hydrogenating the corresponding halogen-substituted nitroaromatic compound in the presence of a platinum group metal catalyst, said catalyst being modified with a metal 52 U.S. c1 ..260/580, 260/296 R, 260/518 A, Selected from the group Pb, Bi or As. The catalysts are effw 252/472 252/474 tive at relatively mild conditions and the hydrogenation is ef- [5 l Int. Cl ..C07c 85/10 fected with minimum dehalogenatiom [58] Field of Search ..260/580 6 Claims, No Drawings PROCESS FOR PREPARING AROMATIC HALOAMINES FROM AROMATIC NITROAMINES BACKGROUND OF THE INVENTION It is known that nitro-submitted aromatic compounds can be effectively reduced to aromatic amines in the presence of various catalysts, including precious metal catalysts. However, where the nitro compound contains an aromatic halogen, reduction of the nitro group without dehalogenation presents a particularly difficult problem. The halogen is labilized by both the nitro function and by the amino function and usually extensive hydrogenolysis of the halogen group occurs during the catalytic reduction of the compound. The extent of concomitant or subsequent dehalogenation depends, among other things, on the halogen increasing generally in the order fluorine, chlorine, bromine and iodine.

Heretofore the use of special catalysts has been proposed as a method of reducing hydrogenolysis of the halogen group. Of the precious metal catalysts, it is known that palladium gives extensive hydrogenolysis whereas platinum and rhodium give less. To reduce the extent of hydrogenolysis the catalysts, particularly platinum and rhodium, have been modified. Among the catalysts proposed for this purpose, for example, are sulfided platinum catalysts, magnesium oxide or magnesium hydroxide promoted platinum catalysts, and calcium hydroxide promoted rhodium catalysts. None of the catalysts previously proposed are completely satisfactory, each having its own particular limitations. For example, in processes employing platinum on carbon in conjunction with an oxide or hydroxide of magnesium, the catalyst and additive concentrations must be maintained within narrow critical limits otherwise extensive dehalogenation occurs. Sulfided platinum, although satisfactory for certain applications has poor activity in lower temperature ranges required in some systems, such as those subject to decarboxylation or to polymerization.

It has now been found that platinum group metals modified by certain heavy metals are effective in selectively reducing halogen-substituted nitroaromatics to the corresponding amines with a minimum of hydrogenolysis of the halogen. It has also been found that these heavy metal modified catalysts are particularly effective at lower temperatures than previously practicable.

THE INVENTION ln accordance with the present invention halogen-substituted nitroaromatics are reduced to the corresponding haloamines by hydrogenation in the presence of a platinum group metal modified with a metal selected from the group lead, bismuth and silver. Preferably the platinum group metal is platinum or palladium. In preferred embodiments the catalyst is platinum or palladium modified with a heavy metal acetate, particularly lead acetate.

The modified platinum group metal is preferably supported on a carrier. Suitable carriers are carbon, alumina, barium carbonate, barium sulfate, calcium carbonate, kieselguhr, silica, and preferably the carrier is carbon. The supported catalysts used in this invention can be prepared by any of the methods known in the art. Thus, the catalysts may be prepared by precipitation or absorption, i.e. the metals may be coprecipitated or one metal may be precipitated after the other metal is absorbed on a support. The metals may also be absorbed together or one metal may be absorbed after the other is on the catalyst support. Either in the preparation or during the hydrogenation process a reductive effect on the catalyst occurs, so that the platinum group metals and the modifying metals may be wholly or partially reduced to the metal.

One suitable method for preparing the modified catalyst is as follows: To an aqueous suspension of a platinum group metal supported on a carrier, e.g. platinum on carbon, is added, while stirring, a soluble compound of lead, bismuth, or silver, e. g. lead acetate, bismuth subacetate, lead nitrate, silver nitrate, silver lactate and bismuth citrate, or mixtures thereof. The stirring is continued after the addition is complete for an interval of about 5 minutes to an hour, after which the composite is filtered and then dried overnight at about l00 C. to yield the modified catalyst.

Supported platinum group metal catalysts, e.g. platinum on carbon are readily available commercially or they can be prepared by methods well known in the art for the preparation of a highly dispersed platinum group metal on a support. For example, platinum on carbon may be prepared by dispersing finely divided activated carbon in water containing a soluble platinum compound and the platinum precipitated on the carrier as the oxide or hydroxide. Then the catalyst composite is filtered, washed and dried. The platinum compound can be reduced to the free metal prior to or after washing using known reducing techniques, e.g. by treatment with formaldehyde, hydrogen, etc.

In the catalysts of this invention, the platinum group metal is present on the support in an amount of about 0.1 to 10 percent of the total catalyst weight including the support, and preferably about 1 to 8 percent by weight. The upper level of the platinum group metal is about 10 percent because of cost considerations. It has been found convenient for exemplary purposes to employ a catalyst containing 5 percent by weight platinum group metal. The modifying metal, i.e. Pb, Bi or Ag, is present in an amount of about 0.1 to 10 percent by weight based on total catalyst, and preferably about 1 to 8 percent by weight. Preferably the weight relationship of the platinum group metal to the modifying metal is about 1:0.5-2.

The catalysts may be granular, extruded or pelleted if used as stationary catalysts, as in a continuous process, or preferably powdered if used in a batch process. Generally, in the process of this invention the catalyst is employed, in batch processing in the amount of about 0.1 to 10 percent by weight, based on the weight of the halonitroaromatic substrate being treated.

The reaction temperature for hydrogenation is in the range of about 25 to 250 C., preferably about 50 to C. The pressure is in the range of about 0 to 5,000 psig, preferably about 50 to 500 psig. The selection of particular reaction conditions including the temperature, pressure and catalyst concentration will vary within the aforesaid limits depending to a certain extent on the halonitroaromatics being treated. As noted above, the extent of lability of the halogen varies, for example, the bromo compounds are in general more prone to hydrogenolysis than the corresponding chloro or fluoro compounds. Also, it is well known that the lability of the halogen is dependent upon the position in the ring relative to the nitro group. Since the undesired hydrogenolysis reaction occurs more readily at high temperatures and pressures, it is preferred to employ the mildest effective conditions within the ranges taught above. It is an important feature of the catalysts used in the present invention that they exhibit high activity at relatively lower temperatures than previously known highly selective catalysts used in the process and, therefore, lower temperatures can be employed in the process than previously practicable. Other catalysts can be used at lower temperatures but they are not as selective as those of the present invention.

The selective reduction is conducted in a liquid phase solution of the halonitroaromatic dissolved in a suitable solvent. Inert organic liquids are employed as solvents. Illustrative solvents are lower aliphatic alcohols such as methanol, ethanol, isopropanol, t-butanol, hydrocarbons such as cylcohexane, octane, lower alkanoic acids such as acetic acid and propionic acid, ethers such as dioxane, and tetrahydrofuran, etc. Although reduction of the substrate will occur in the absence of a solvent, from practical considerations it is highly desirable to use one in order to improve the rate of reaction and to dissipate the heat evolved in the process. Since the halonitroaromatics are generally solids at room temperature, the use of a solvent adds to the convenience in operating the process. Generally, the concentration of solvent is varied between about 20 to 90 percent by weight solvent based on the solvent plus reactant weight. Typically the process is carried out by charging the reaction vessel with the substrate, solvent and catalyst and then passing hydrogen through the system or agitating the charge with hydrogen under pressure. The product may be separated or recovered by known methods such as fractional distillation, preparative chromatography with hydrogen and finally pressurized with hydrogen and heated. The hydrogcnations generally were allowed to proceed for 20 minutes. The time when about 3 moles of hydrogen was absorbed was noted. This corresponds to and recrystallization. theoretical formation of chloroaniline. After termination of The process of the present invention can be employed for the reaction, the catalyst was removed by filtration and the tilthe production of substantially any aromatic haloamine, for trate was analyzed by chromatographic techniques. Represenexample, haloanilines such as o-chloroaniline, mtative results are given in the Table. in tests I through 10, the bromoaniline, p-fluoroaniline, 2,3-, 2,4- and 3,4- platinum group metal catalyst contains 5 percent Pt on cardichloraniline, and the like; haloaminophenols such as 3- bell, and n tests 1 1 and 12, he pla inum group metal catalyst bromo-, 3-chloroor 3-fiuoro-4-aminophenol, 2,3-dichloro-4- Contains 5 P Pd carbon aminophenol, etc., halodiphenylamines such as 4-tluoro, 4- The data n h Table how that halogen-substituted chloroor 4-brom0-diphenylamine; alkylhaloanilines such as hih'oaromatie compounds y be selectively hydrogenated at 4 h| -2 i d h lik h l i h l relatively low temperature and pressure conditions in the aliphatic acids such as 6-chloro-2-amino benzoic acid, etc., Presence of a Platinum metal catalyst modified with lead, halonitronaphthalenes such as l-chlor0-2-nitronaphthalene, bismuth or silver acetate, to Yield the Corresponding halogenl-nitro-2-fluoronaphthalene, etc. For the preparation of such Substituted el'omatie amine? example, in Test 4 halo-substituted aromatic amines the corresponding halo-subg 3 Prior art suifided Platinum y the i to rb 3 i d aromatic nitro compound i d moles of hydrogen per mole of substrate took over 10 times Th aromatic h l i prepared b h present process longer than that required in Test No. 6 (using a lead modified are useful as dyes, dye intermediates, insecticides and fungi- Platinum emdiyst Of this invention), although Test 6 s cides. For example, chloroanilines are used in the preparation huh with 5/3 the catalyst loading and at a lower temperatureof azo dyes.

The invention will be further illustrated by reference to the EXAMPLE 2 f ing X P In the experiment of this example the hydrogenation is carried out using the procedure and equipment described in Ex- EXAMPLE 1 ample 1, except that the substrate is 10.0 grams of 3-chloro-6- This example demonstrates the selective hydrogenation of methoxyamitropyridine and the Solvent is 25 m1 of acetic chloronitrobenzenes to the corresponding chloroanilines in acid- The hlf usedis 300 mg lead-modified Platinum 011 the presence of a metal acetae modified piafinum meta] carbon containing 5 percent lt and 5 percent Pb. The test is hydrogenation catalyst. For purposes of comparison tests were run at 990 and 1,000 psig and the iota! absorption of conducted using a commercially available platinum on carbon hydrogen approaches 3 i The hydrogen catalyst, a sulfided platinum catalyst and platinum catalysts rate ml OfH? Per mmute- Product ahaiysls by gas'hquld modified with bismuth, lead, silver, magnesium and copper chromotography shows 9" Percent of the Corresponding acetates according to the method detailed below. Tests were 3chiorosubsmuted ammopyndme and he hydrogehoiysis Of also conducted with lead acetate modified palladium on carthe halogen" bon catalyst. EXAMPLE 3 a. Catalyst Preparation To 135 ml of H 0 was added 15 g of 5 percent platinum on 40 In the experiment of this example the hydrogenation is carcarbon. The suspension was stirred while 15 ml of a 5 percent ried out using the procedure and equipment described in Exlead acetate solution was added over about a 5 minute period. ample 1, except that the substrate is 5.0 grams of l-nitro-5,8- After the addition was complete the mixture was stirred for a dichloronaphthalene, the solvent is 30 ml of isopropanol, and bi hour, filtered and then dried overnight at l 10 C. to yield the lyst i 500 mg of a lead-modified platinum on carbon the modified catalyst. catalyst containing 5 percent Pt and 5 percent Pb. At 100 C. In the same manner bismuth sub-acetate, silver acetate, and 750 psig the hydrogen uptake is 173 ml per minute and magnesium acetate and copper acetate were employed to hydrogenation virtually stops at an uptake of 3.0 moles of prepare magnesium and copper modified platinum catalysts. hydrogen. Product analysis by gas-liquid chromotography Also, a 5 percent palladium on carbon catalyst was modified Shows ver 98 percent l-amino-S,B-dichloronaphthalene. by this general procedure. what is claimed 15! Hydrogenation l. A process 5,000 producing aromatic haloamines which The hydrogenation was conducted by charging a Pyrex test comprises hydrogenating a chloronitroaromatic compound tube containing a stirring bar with 25 ml of isopropanol, 200 Selected from the group Consisting of ehiofonitmbenlene, 600 mg of catalyst and 10 g of the chloronitrobenzene subdiehloi'ohitrobehzehe and ehiomhih'ohaphthaiene in the strate. The test tube was placed in a stirred autoclave, flushed iq Phase at a p in the range of about to TABLE Time to absorb 3 Hydro- Amt. oi Halogenated moles H Total l. catalyst} Catalyst nitrobenzene Press, Temp, mole subtime, ysis, Test No. mg. modifier substrate psig. C. smite, min. min. Substituted aniline percent 300 None 2,5-clichl0ro 750 76 12 100 200 5% Cu 3-chl0r0 770 T8 15 200 5% Mg ..do 750 75 11 0 600 Sulfur 2,5dichlor0 750 100 90 2,5 dichl0ro 1 300 1% Pb .dO 750 75 ll 20 90% 2,5(iichl0r0 10 200 750 76 8 20 99% 2,5-dichlor0 1 200 750 77 14 20 85% 3-chloro 15 200 760 7 12 20 93% 3-chl0r0 1 200 750 75 9 2O 95%3-ch10r0 5 200 750 75 16 30 d0 5 600 750 77 2 15 None (300 5% Pl) d0 750 100 ll 20 99% 3-t:lll0ro None 1 'lesls ll(l contain 5% Pt on carbon and Tests 11 ninl 12 contain 5% Pd on carbon.

1 Not modified-"WE? lt on carbon.

(Oinlnmvinlly nvnilnblv snllidvil Pl ('nlnlyst containing 5% Pl. on carbon.

Not modiflml- 5'1;- l'il on carbon.

C. and a pressure in the range of about to 5,00 psig in the product of the hydrogenation.

presence of a catalyst consisting of from 0.1 to 10 percent by 2. The process of claim 1 wherein said solid carrier is carweight, based on the total weight of catalyst, of a first metal b selected from the group consisting of platinum and palladium, 3 The process f Claim 2 wherein said fi metal is and from 0.1 to 10 percent by weight, based on the total 5 weight of catalyst, of a modifying metal selected from the group consisting of lead, bismuth and silver, said first metal and said modifying metal being supported on a solid carrier and the weight ratio of said first metal to said modifying metal being from 120.5 to 1:2, effecting said hydrogenation until about 3 moles of hydrogen per mol of said chloronitroaromatic compound are absorbed, and recovering the corresponding chloroaromatic amine as the sole substantial platinum and said modifying metal is lead.

4. The process of claim 2 wherein said first metal is palladium and said modifying metal is lead.

5. The process of claim 2 wherein said first metal is platinum and said modifying metal is bismuth.

6, The process of claim 2 wherein said first metal is platinum and said modifying metal is silver. 

2. The process of claim 1 wherein said solid carrier is carbon.
 3. The process of claim 2 wherein said first metal is platinum and said modifying metal is lead.
 4. The process of claim 2 wherein said first metal is palladium and said modifying metal is lead.
 5. The process of claim 2 wherein said first metal is platinum and said modifying metal is bismuth.
 6. The process of claim 2 wherein said first metal is platinum and said modifying metal is silver. 